INSIDIOUS Synonyms: 100 Similar and Opposite Words

insidious

adjective

Definition of insidious

as in treacherous

formal causing harm in a way that is gradual or not easily noticed Most people with this insidious disease have no idea that they are infected. an insidious enemy

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Example Sentences

Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.

Recent Examples of insidious In my view, statements to that effect are shortsighted, prioritizing short-term social effects over more insidious and long-term issues, including addiction. — Emma Fenske, The Conversation, 2 July 2026 The narrative chronicled an international gang of scientists and military folks that stumble across a Stargate network deep in the Pegasus Galaxy and its insidious alien antagonists called The Wraith. — Jeff Spry, Space.com, 17 June 2026 This reflects a larger and perhaps insidious problem in the United States, where there’s been an erosion in trust in public health, in doctors and in the medical profession as a whole. — Joshua P. Cohen, Forbes.com, 13 June 2026 Speaking of pop music, while the new ad format is expected to have its critics, there’s a far more insidious change afoot in that Green and Pleasant Land. — Anthony Crupi, Sportico.com, 12 June 2026 See All Example Sentences for insidious

Recent Examples of Synonyms for insidious

Adjective

If the institutions managing climate risk are instruments of a cosmic power consolidating control over humanity, the question of whether a carbon price is well-designed becomes not just wrong but spiritually treacherous.

— Nick Lichtenberg, Fortune, 18 July 2026
The only thing more treacherous than his journey home might be tackling a ranking of Nolan's filmography.

— Brian Truitt, USA Today, 17 July 2026

Definition of treacherous

Adjective

But Scheft and his team are mastering the subtle differences and plan to offer many of the same loaves available in Boston, though the bakeries will have a few different offerings.

— Connie Ogle July 17, Miami Herald, 17 July 2026
In one of Nolan’s subtle but important additions to Homer’s tale, all throughout the film, everyone expresses fears about the People from the Sea, this unseen menace terrorizing different towns.

— Bilge Ebiri, Vulture, 17 July 2026

Definition of subtle

Adjective

Judge Ranjan identified several problems with MET’s claims, including MET’s allegation that UA engaged in false advertising by portraying Celliant as having the FDA’s blessing.

— Michael McCann, Sportico.com, 15 July 2026
Coney Barrett shared her experience bringing home a bulletproof vest and having her house swatted, or subject to false police reports.

— Emma Hinchliffe, Fortune, 15 July 2026

Definition of false

Adjective

The standout interlude is the soldiers’ visit to the island domain of Circe, a treacherous witch played with deceptive calm and a misleading air of distraction by a bone-chilling Samantha Morton.

— David Rooney, HollywoodReporter, 15 July 2026
Using a clinician’s name, image, or credentials in a synthetic endorsement without consent should be treated as deceptive practice, with liability directed toward those who commission or distribute the content.

— Henry Bair, STAT, 14 July 2026

Definition of deceptive

Adjective

At the World Cup, there were at least six examples of incorrect or — to be generous — highly dubious interventions that made reasonable on-field decisions worse across the 104 matches.

— Graham Scott, New York Times, 22 July 2026
In September, the Michigan Department of Health and Human Services sent a notice denying her coverage, citing incorrect income information and stating she wasn't disabled, according to Kolosova and state documents reviewed by KFF Health News.

— Rachana Pradhan, NPR, 20 July 2026

Definition of incorrect

Adjective

First, the medals were the wrong colour; this was the ‘Bronze Final’ after all.

— Jack Pitt-Brooke, New York Times, 19 July 2026
That turned out to be wrong for a meaningful minority of them, whose brains were generating signals our methods were not sensitive enough to pick up.

— Torie Bosch, STAT, 18 July 2026

Definition of wrong

Browse Nearby Words

inside tracks

insidious

insidiously

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“Insidious.” Merriam-Webster.com Thesaurus, Merriam-Webster, https://www.merriam-webster.com/thesaurus/insidious. Accessed 23 Jul. 2026.

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Synonyms of insidious

adjective

Example Sentences

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